DRASTIC-Based Methodology for Assessing Groundwater Vulnerability in the Gümüşhacıköy and Merzifon Basin (Amasya, Turkey)

EARTH SCIENCES RESEARCH JOURNAL

Earth Sci. Res. SJ. Vol. 17, No. 1 (June, 2013): 33 - 40

HYDROGEOLOGY DRASTIC-based methodology for assessing groundwater vulnerability in the Gümüşhacıköy and Merzifon basin (Amasya, Turkey)

Arzu Firat Ersoy* and Fatma Gültekin*

*Karadeniz Technical University, Engineering Faculty, Geological Engineering Department, 61080, Trabzon, Turkey Corresponding author: Arzu FIRAT ERSOY e-mail:[email protected] phone: + 90 462 377 20 63 fax: + 90 462 325 74 05

ABSTRACT Key words: Vulnerability Mapping, DRASTIC, Geographic Information System (GIS), Turkey Preparing aquifer vulnerability maps has become crucial during recent years for preventing adding new ones to aquifers which have been contaminated due to environmental effects and been out of use. GIS techniques and DRASTIC method were used when preparing vulnerability maps for the basin in which the Gümüşhacıköy and Merzifon aquifers are located. Groundwater flow is approximately directed west-east and many villages are located across the aquifer in the basin which contains two sub-provinces and is characterised by intensive agricultural activity. DRASTIC layers were created when preparing vulnerability map, using parameters such as groundwater level, recharge, aquifer environment, topography and hydraulic conductivity. The aquifer vulnerability map was prepared by overlapping the layers by means of GIS. , three different vulnerability zones were determined in the Gümüşhacıköy basin according to DRASTIC scores low (<100), medium (100-140) and high (>140). Based on the vulnerability map, it was found that the Gümüşhacıköy Basin had a low contamination potential. It was established that 16% of the basin had high vulnerability and 47% low vulnerability. Areas having high vulnerability generally overlapped areas where the slope was gentle soil above the aquifer was permeable.

RESUMEN Palabras claves: Mapa de vulnerabilidad, DRASTIC, Sistema de información Geográfica (GIS), Turquía. La preparación de mapas de vulnerabilidad acuífera se ha convertido en una actividad crucial en los últimos años para prevenir la contaminación por efectos ambientales de un afluente y su posterior inuti- lización. Técnicas GIS y el método DRASTIC fueron utilizados en la preparación de mapas de vulnerabilidad en la cuenca donde están localizados los acuíferos Gümüşhacıköy y Merzifon, en Turquía. El flujo de las aguas subterráneas corre aproximadamente Oeste-Este y varias poblaciones están ubicadas al paso del acuífero por dos subprovincias que se caracterizan por la actividad agrícola. Se crearon capas en el mé- todo DRASTIC cuando se preparó el mapa de vulnerabilidad con parámetros como nivel, recarga, am- biente del acuífero, topografía y conductividad hidráulica. La representación de vulnerabilidad se logró al sobreponer estas capas a través de técnicas GIS, lo que permitió determinar tres zonas diferentes de vulnerabilidad en la cuenca de Gümüşhacıköy basado en los puntajes del método DRASTIC: baja (<100), medio (100-140) y alta (>140). Con base en este mapa, se concluye que la cuenca de Gümüşhacıköy Record tiene un bajo potencial de contaminación. Se estableció que el 16 % de la cuenca es altamente vulnerable y el 47 % de baja vulnerabilidad. En aquellos lugares identificados con alto potencial de contaminación Manuscript received: 23/10/2012 se suelen sobreponer áreas donde la inclinación de tierra sobre el acuífero es permeable. Accepted for publication: 04/04/2013

Introduction the use of fertilisers and pesticides. Vulnerability assessment has been re- cognised for its ability to delineate areas which are more easily contamina- Groundwater has been considered as an important source of water ted than others as a result of anthropogenic activity on/or near the earth’s supply due to its relatively low susceptibility to pollution compare to sur- surface. Vulnerability studies can thus provide valuable information for face water. Groundwater quality is usually subject to contamination es- stakeholders working on preventing further deterioration of the environ- pecially in agriculture-dominated areas having intensive activity involving ment (Mendoza and Barmen 2006). Arzu Firat Ersoy and Fatma Gültekin

Figure 1. Location map of the Gümüşhacıköy-Merzifon basin (GMB) DRASTIC-based methodology for assessing groundwater vulnerability in the Gümüşhacıköy and Merzifon basin (Amasya, Turkey)

The concept of groundwater vulnerability to contamination was in- layer thickness ranges from 10 to 50 cm in these series. The very loose troduced in the 1960s in France by Margat (1968). Several approaches layers are not continuous and change their lithology over short distances. for developing aquifer vulnerability assessment maps were adopted such This unit gradually become harder as one goes deeper and turns out to as DRASTIC (Aller et al. 1987), GOD (Foster 1987), AVI (Van Stemp- be conglomerate. Some blocks of the gravels are 50 cm thick and about voort et al 1993), and SINTACS (Civita 1994). Conventional methods 5-10 cm-in diameter 95% of such gravel and blocks are usually rounded (i.e. DRASTIC, AVI, GOD, SINTACS) can distinguish degrees of vulne- and are composed of volcanic material. The Quaternary is characterised by rability on a regional scale involving different lithology (Vias et al 2005). alluvium and an alluvium cone consisting of detrical material that comes DRASTIC is a familiar method developed for the US Environmental Pro- from north and south with the flood waters. Alluvium and cone (10-60 m tection Agency (EPA) by Aller et al (1987) it has been used in several thick) take the form of gravel, sand, clay and a mixture of these, along the regions (Merchant 1994; Melloul and Collin 1998; Cameron and Peloso Gümüşsuyu, Köseler and Salhan Rivers. 2001; Al-Adamat et al 2003; Baalousha 2006; Jamrah et al 2007; Sener et al 2009; Massone et al 2010). Hydrogeology The area studied in this research is located in Amasya (mid Black Sea region), namely the Gümüşhacıköy-Merzifon Basin (GMB) (Figure 1). The GMB’s hydrogeological setting has been outlined by Fırat Ersoy Groundwater is the major source of irrigation in the Amasya District in (2007). The most impotant geological units for groundwater transport in Turkey. Surface water has been the main source of water supply for irriga- the basin are Quaternary alluvium and Pliocene clay, sand, gravel and a tion during the last few decades (Fırat Ersoy and Gültekin 2008). Howe- mixture of these. Unconsolidated Quaternary and Pliocene sediments are ver, water demand has increased and groundwater is now used as a secon- around 350 m thick. The other units underlying the alluvium do not bear dary source. Annual groundwater exploitation yield was only 3.5x106m3 significant amounts of groundwater. The GMB can be divided into discre- during the 1970s, and rose to 5.5x106 m3 in 2005 (Fırat Ersoy, 2007). Due te hydrogeological units, including permeable (alluvium), semi-permeable to the excessive exploitation of groundwater, water levels have significantly (weak cemented pebble and sandstone, silty clay and volcanic rocks) and decreased. Groundwater quality has also been affected by over exploitation. impermeable (massive marble and limestone, silty clay and schist). The town of, Gümüşhacıköy is located in this basin. Some well water’s Alluvial materials and the Pliocene units consisting loosely cemented nitrate concentration has reached 15.6 mg/l in the Gümüşhacıköy Basin. pebbles, sand and clayey-silt materials outcrop in most parts of the basin. Nitrite and ammonium concentration have reached 0.03 and 0.3 mg/l Known as the Gümüşhacıköy aquifer, this part is crucial to groundwater respectively, around the town (Fırat Ersoy et al, 2006). storage and transfer since it is characterised by high conductivity and sto- This paper was aimed at assessing groundwater vulnerability to pollution rage capacity. Deposits have a heterogeneous structure, being formed as in a shallow aquifer using the DRASTIC model and geographical informa- alluvial cones at the end of tributary rivers. The alluvial cone formed by tion system (GIS) techniques combined with hydro-geological data layers, i.e. the alluvial unit of the Paşa and Yakacık river is called the Merzifon aquifer. depth of water, net recharge, aquifer media, soil media, topography, impact of Well logs show that the cone’s middle sections consist of clayey levels bet- vadose zone and hydraulic conductivity. A vulnerability map, showing high, ween pebble and sand layers and that level becomes thin along the eastern medium and low vulnerability areas was produced for the mentioned basin. edge, dominated by clay and silt. Since the section between the east of the Gümüşhacıköy aquifer and the south of the Merzifon aquifer consists of Study area Miocene clay and marl, it is not important in terms of groundwater. The Late Eocene volcanic rocks outcropping across the north, nor- The GMB covers a 1,060 km2 area elevation ranging from 550- 1,873 thwest and northeast of the basin form a catchment area with their frac- m (Figure 1). Average annual rainfall is 458 mm average annual temperatu- tured and fissured structure. Natural discharge in the basin is provided by re is 13.6°C (URL-1) and the average annual potential evaporation is 680 a stream flowing through it from west to east. The Gümüşhacıköy aquifer mm (Fırat Ersoy, 2007). The most important body of surface water flowing naturally discharges into the Gümüşsuyu river, located in the east of basin. through the basin is the Gümüşsuyu River, which discharges 8.5x106m3/ The basin contains numerous springs discharging from geological year (Fırat Ersoy, 2007). Groundwater in the basin draws from both allu- units, faults and fractures. Some are exploited as potable for drinking water vium aquifers, one being confined, (the Gümüşhacıköy aquifer) and the and others are used for irrigation, consequently recharging the ground- other unconfined (Merzifon). Agriculture is widespread in the basin, and water. The springs’ total flow rate is 720 l/sec. fertiliser and pesticide application have caused groundwater contamina- Three ponds in the basin are used for irrigation. Infiltration into the tion through leaching. 193 wells had been drilled in the GMB up to 2006, groundwater from these ponds has been estimated as being 41.5 m3/year 173 wells were aimed at irrigation, and 20 well for domestic purposes. on average (Fırat Ersoy, 2007). The basin contains 193 wells, 167 in the Gümüşhacıköy aquifer Geology and 26 in the Merzifon aquifer (DSİ, 2006). Well depth varies from 39 to 290 m and pump flow-rates from 5 to 60 l/sec (DSİ, 2006). As The Paleozoic metamorphic rocks in the study area, represent the most of these wells are used for irrigation, pumps operate from May to oldest formation. These rocks consist of clayey schist, chlorite schist and October. The increased number of wells drilled in the aquifer during green schist, marble and re-crystallised limestone. Upper Jurassic-Lower recent years and accordingly, the increased amount of water pumped Cretaceous limestone, in the area has fossils which are generally compact, from the aquifer has resulted in a decrease in groundwater level by 15 thick-bedded, very hard and fissured lower Cretaceous limestone is pink, to 20 m (DSI, 2006). very hard, thick bedded and micritic, overlying Jurassic limestone. Cre- Several pumping tests have been performed at existing wells in the taceous limestone outcrops on the plain. The flysch series having mixed Gümüşhacıköy and Merzifon aquifers. Data interpretation has indicated 89.7- volcanic material composed of conglomerate, green and black sandstone, 1727 m2/day transmissivity, 0.76- 19.17 m/day hydraulic conductivity and shale, marl, limestone, andesite, tuff and tuffite are deposited in the Upper 1.5x10-5- 7.9x10-3 storage coefficient for the basin (Fırat Ersoy, 2007). Cretaceous limestone. Cenozoic beds started with the Middle Eocene age flysch series in the study area. Flysch consists of sandstone, shale, sandy Materials and Methods limestone, marl, local conglomerate, tuff and agglomerate. The Miocene series consist of thick blue claystone and marl and the Pliocene beds of DRASTIC, proposed by the US Environmental Protection Agency micro conglomerate, sandstone, sand, clay, gravel and a mixture of these (Aller et al., 1987) and its modification termed SINTACS (Civita, 1994), Arzu Firat Ersoy and Fatma Gültekin

Table 1 DRASTIC Weighting factors (Aller et al. 1987)

Relative Parameter Range Rating Description weighting 0-5 10 Refers to the depth to the water surface in 5-15 9 an unconfined aquifer. Deeper water table 15-30 7 Depth to water (D) levels imply lesser chance for contami- 30-50 5 5 (feet) nation to occur. Depth to water is used 50-75 3 to delineate the depth to the top of a 75-100 2 confined aquifer. >100 1 Indicates the amount of water per unit 0-2 1 area of land which penetrates the ground 2-4 3 Net recharge (R) surface and reaches the water table. 4-7 6 4 (in) Recharge water is available to transport a 7-10 8 contaminant vertically to the water table, >10 9 horizontal with in an aquifer. Massive shale 2 Metamorphic/igneous 3 Refers to the consolidated or unconsoli- Weathered met./igneous 4 dated medium which serves as an aquifer. Bedded sandstone, Limestone, The larger the grain size and more fractu- Shale sequences 6 Aquifer media (A) res or openings with in an aquifer, leads to 3 Massive sandstone 6 higher permeability and lower attenuation Massive limestone 6 capacity, hence greater the pollution Sand and gravel 8 potential. Basalt 9 Karst limestone 10 10 Soil thin or absent 10 Gravel 9 Refers to the uppermost weathered Sand 8 portion of the vadose zone characterised Peat 7 by significant biological activity. Soil Shrinking and/or aggregated clay Soil media (S) 4 has a significant impact on the amount 2 Sandy loam 5 of recharge which can infiltrate into the LoamSilty loam 4 ground. Clay loam 3 Muck 2 Non-shrinking and non-aggregated clay 1 0-2 10 Refers to the slope of the land surface. 2-6 9 Topography (T) It helps a pollutant to runoff or remain 6-12 5 1 (slope%) on the surface in an area long enough to 12-18 3 infiltrate it. >18 1 1 Silt/clay 3 Shale 6 Limestone 6 Is defined as unsaturated zone material. Sandstone 6 The significantly restrictive zone above Impact of vadose Bedded limestone, Sandstone, shale an aquifer forming the confining layers is 5 zone (I) Sand and gravel with significant silt and clay 6 used in a confined aquifer, as the type of Metamorphic/igneous 4 media having the most significant impact. sand and gravel 8 Basalt 9 Karst limestone 10 1-100 1 Refers to the ability of an aquifer to trans- 100-300 2 Hydraulic conducti- mit water, controlling the rate at which 300-700 4 vity (C) (GPD/ft2) groundwater will flow under a given 3 700-1,000 6 hydraulic gradient. 1000-2,000 8 material within the groundwater system >2,000 10 DRASTIC-based methodology for assessing groundwater vulnerability in the Gümüşhacıköy and Merzifon basin (Amasya, Turkey) are two methods for evaluating vertical vulnerability based on the fo- gital elevation model (DEM).Groundwater table depth changed between 9-40 llowing seven parameters: depth to water (D), net recharge (R), aquifer m in the GMB the Merzifon aquifer has the lowest groundwater depth in media (A), soil media (S), topography (T), vadose zone impact (I), and the GMB. The deepest groundwater occurred at the end of the impermeable hydraulic conductivity (C) Figure 2). Each mapped factor is classified into layer over the aquifer media in the mostly confined Gümüşhacıköy aquifer. ranges (continuous variables) or significant media types (thematic data) The depth to water table map was then classified into ranges defined by the having an impact on pollution potential. Weighting multipliers are then DRASTIC model and assigned rates ranging from 1 (minimum impact on used for each factor to balance and enhance their importance, the typical vulnerability) to 10 (maximum impact on vulnerability) (Figure 3). rating ranging from 1 to 10 (Table 1). The final vulnerability index is a weighted sum of the seven factors.

The DRASTIC index (Di) can be computed using expression (1): Di = Dr Dw + RrRw + ArAw + SrSw + TrTw + IrIw + CrCw (1) Di DRASTIC index for a mapping unit w weighting factor for each parameter r rating for each parameter D, R, A, S, T, I, and C the seven parameters

Figure 3. Depth to water table map of the study area

Net recharge (R)

Net recharge is the total quantity of water infiltrating from ground surface to an aquifer on an annual basis. Local recharge in the study area comes from inflow by the Gümüşsuyu river and its branches, irrigation return flow and direct recharge. The main groundwater recharge source are the Gümüşsuyu River, springs, located high in the basin, and irrigation leakage. The average direct annual volume of recharge into the aquifer from the surface of the basin and from the springs is about 11334316 m3 (Fırat Ersoy, 2007). Irrigation pond canals contribute 41.5 m3 recharge in the area (Fırat Ersoy, 2007) the recharge map was then classified into ranges and assigned ratings from 1 to 8 (Figure 4).

Figure 2. DRASTIC Method flowchart

Results

Depth to water (D)

Depth to water is defined as the distance (in meters) from the ground surface to the water table. Groundwater table depth in the GMB has been measu- red since 1976. This present study, has used the 2005 values for groundwater table depth. The 167 wells’ location was digitised from the accompanying di- Figure 4. Net recharge map of the study area Arzu Firat Ersoy and Fatma Gültekin

Aquifer media (A)

Aquifer media refers to consolidated or unconsolidated rock which serves as an aquifer. The main aquifer being exploited and that most vulnerable to contamination is partially confined, here called the Gümüşhacıköy aquifer the central and northern parts of the Gümüşhacıköy aquifer are confined. The clayey layer over high permeability uncemented sediments is 2- 10 m thick from the drilling data. Clayey layer thickness of gradually changes from the centre to the north of the basin. The Merzifon aquifer is unconfined. The aquifer media was obtained using a subsurface geology map, geological sections, and drilling profiles of the Gümüşhacıköy and Merzifon aquifers. The main aquifer includes Quaternary alluvium and Pliocene gravel, sand and clayey levels. The Merzifon aquifer’s alluvial fan is relatively thin, consisting of coarse-grained gravel and sand with silt and clay interbeds. The aquifer media were mapped as shown in Figure 5.

Figure 6. Soil media map of the study area

Figure 5. Aquifer media map of the study area

Soil media (S)

Soil media refers to the uppermost portion of the vadose zone cha- Figure 7. Topography map of the study area racterised by significant biological activity. Soil plays a significant role in the amount of recharge which can infiltrate into the ground and hence Vadose zone impact (I) on a contaminant’s ability to move vertically into the vadose zone. A soil’s pollution potential is largely affected by the type of clay present, such clay’s The vadose zone is defined as the zone above the water table which is shrink/swell potential, and soil grain size. Soil media in the GMB was unsaturated. Unconsolidated clayey gravel and sand represents the vadose determined using drilling profiles. The Gümüşhacıköy and Merzifon aqui- zone in the plain, volcanic rocks and limestone is the vadose zone in the fers are covered by clayey gravel and sand and alluvial plains. Fractured mountain areas. The map of vadose zone impact is shown in Figure 8. volcanic rocks are located west and south-west of the GMB and limestone outcrops south of the basin. Thickness over the volcanic rock and limesto- The aquifer’s hydraulic conductivity (C) ne gradually changes form bottom to top, the hills especially, having little or no soil. The soil media map was then classified into ranges and assigned Hydraulic conductivity is important because it controls the rate of ratings from 3 to 10 (Figure 6). groundwater movement in the saturated zone, thereby controlling the degree and fate of contaminants. Hydraulic conductivity values used in this Topography (T) study were derived from pumping test data. Hydraulic conductivity varied from 8.79 × 10−6 to 2.21 × 10−4 m/s in alluvium (Fırat Ersoy, 2007). The Topography refers to land surface slope variability. Slope degree will hydraulic conductivity of the other rock in the basin was available from the determine the extent of pollutant runoff and settling long enough to pertinent literature. Hydraulic conductivity values for various rock types infiltrate. A digital elevation model (DEM) was used to extract the slope have been proposed by Domenico and Schwartz, (1990). The hydraulic of the study area, while 27% of the GMB has a gentle slope, most of the conductivity of the limestone and fractured volcanic rocks, located in the basin has a steep slope. The areas in the extreme east and south consist west and south part of the basin, were 10-3 m/s and 3x10-4 m/s, respecti- of ridges which may reach 1050 m.. The topography has been mapped vely. Clayey unit permeability is 10−9 to 10−10 m/s. Hydraulic conductivity as shown in Figure 7. rating distribution is shown in Figure 9. DRASTIC-based methodology for assessing groundwater vulnerability in the Gümüşhacıköy and Merzifon basin (Amasya, Turkey)

Figure 8. Vadose zone impact map of the study area Figure 10. Vulnerability index map of the study area

The resulting vulnerability map indicated that the highest potential areas for contamination were the central part of the basin where the slope is gentle. In the southern area where karstic limestone out- cropped, the high DRASTIC index probably represented the effects of aquifer media and hydraulic conductivity. Impermeable volcanic rocks and clay, silty-clay units located in the west and east respectively had low DRASTIC index.

Conclusions

The Merzifon-Gümüşhacıköy (Amasya-Turkey) Basin is an important agricultural centre for the central Black Sea section groundwater is a major water source for such activity. Groundwater quality has de- teriorated due to excessive abstraction of groundwater. This study in- volved using a GIS model and the DRASTIC method for determining the vulnerability of the groundwater in the basin. The aquifer vulnerability map was prepared using depth to water, net recharge, aquifer media, soil media, topography, vadose zone impact, and hydraulic conductivity. The study area was divided into three zones according to Figure 9. Hydraulic conductivity map of the study area groundwater vulnerability assessment results: low (risk index <100); middle (risk index 100–140) and high groundwater vulnerability risk The aquifer vulnerability map (risk index >140). The DRASTIC method results should be useful in designing aquifer The vulnerability map was obtained using the seven hydro-geolo- protection and management strategies. The DRASTIC index map indica- gical data layers in the ArcView GIS software environment. DRASTIC ted that overall potential for groundwater becoming polluted was low for scores ranged from 58 to 177, taking into consideration the determined the GMB. Low sensitivity areas lay outside the agricultural areas in the ratings and weightings. These values were reclassified into three classes basin. The alluvium and most Pliocene sediments were used for agricul- using the Natural Breaks (Jenks) classification method. The study area’s ture in the GMB. The town of Gümüşhacıköy is located on an aquifer vulnerability was classed as low (<100), medium (100-140) and high recharge area. Areas determined by the DRASTIC method should thus (>140) according to data obtained from hydrogeological investigations be given priority in research in terms of contamination. High nitrate con- (Figure 10). centrations were mainly near urban areas according to the the study area’s The GMB’s high groundwater vulnerability risk zones were mainly analysis (Fırat Ersoy et al, 2006). High nitrate concentration was likely to located in the centre of the basin where some villages are located and also be related to wastewater leakage from industrial activities, urbanisation and in the northern and southern parts of the basin. These vulnerable zones agricultural practices. covered around 16% of the studied area. Four springs in the southern area Two towns and many villages were situated in the study area involving had as high vulnerability risk. agricultural activities many wells were used for springs. The prevention of The GMB’s middle groundwater vulnerability risk zones were mainly groundwater pollution caused by waste and wastewater in Gümüşhacıköy’s located in the groundwater recharge area (Figure 10), these vulnerable zo- recharge area was significant owing to groundwater flow being west to east nes covered around 37% of the studied area. The GMB’s low groundwater in the basin. Regarding urban planning and organisation of agricultural vulnerability risk zones were mainly located in the west and south-east of activities in the Merzifon and Gümüşhacıköy districts, the vulnerability the study area (Figure 10), these vulnerable zones covered 47 % of the risk map prepared in the study could be most important when considering studied area. protection off groundwater quality Arzu Firat Ersoy and Fatma Gültekin

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